Unable to Send Email, but can receive it.

[jmair]

I have an ISA 2006 as our proxy. I've published our Exchange 2003 server and we are able to receive all outbound email. We can also send/receive all internal email. But we can't send email to the internet.

To check if DNS is working on my end I've done the following.
Checked the DNS forwarding on my dns server and it also has my ISP DNS ip there. We can access the internet from any location (checking dns again) Also able to ping all servers by machine name, not just by ip. Flushed the Arp on a server and pinged by name again, just to be sure.

I've contacted our ISP, he says everything looks good on their end.

Baffled and a receiving a few calls about the email bounce backs. Any suggestions would be welcome.

[jmair]

*update*
I've tried nslookup on myself and it works fine. But doing an nslookup on an external location fails.

I've added a DNS rule for ISA, from extrenal network to the DNS server.

[ZeroHour]

Right firstly are you going through an external smtp server on your isp or is your smtp server trying to talk to mail servers directly?
Does a telnet to a mx record on port 25 work?
I am assuming exchange has gateway ip etc all set.
What does your current ruleset for isa have?

[jmair]

Right firstly are you going through an external smtp server on your isp or is your smtp server trying to talk to mail servers directly?
Does a telnet to a mx record on port 25 work?
I am assuming exchange has gateway ip etc all set.
What does your current ruleset for isa have?

1:Are you going through an external smtp server on your isp or is your smtp server trying to talk to mail servers directly. The flow would look like this.
www > t1 > firewall > sonicwall > Isa > Exchange Server and Users.

2oes a telnet to a mx record on port 25 work? I tried the following line from telnet, I think this should connect me? (followed instructions from How to Use Telnet to Test SMTP Communication)

Type open mail1.fabrikam.com 25 and then press ENTER.
Connection Failed.
I also tried mine. mail.parkcountyre2.org 25 ... Also failed.


3:I am assuming exchange has gateway ip etc all set. I'm assuming it is also =) . IP flow works fine and haven't seen any issues yet.


4: What does your current ruleset for isa have? Allow DNS to my DNS server. Allow SMTP traffic to Exchange server. Allow outobund SMTP traffic from Exchange server.

[ZeroHour]

I take using telnet to the ip of mail1.fabrikam.com does not work either.
TBH I would be tempted to put a laptop outside ISA to see if you can telnet then to eliminate any upstream filtering.